FIG. 4 is an exploded perspective view of a rotation angle detector of the prior art. Rotary body 51 is disposed in case 52 in a rotatable manner with cylindrical portion 51C inserted in opening 52A. When used in an automobile, a steering shaft (not show in the figure) is inserted in center hole 51D, and rotary body 51 is then engaged with the steering shaft by means of boss 51B.
Detector body 53 is placed rotatably in case 52 in a manner to connect with rotary body 51 through engagement of gear 53A with gear 51A. Permanent magnet 54 is fixed to the center of detector body 53. Another detector body 55 is placed rotatably in case 52, and it connects with detector body 53 through engagement between gears 53A and 55A. The number of cogs of gear 53A differs from that of gear 55A. Permanent magnet 56 is fixed to the center of detector body 55. Wiring board 57 is placed above detector bodies 53 and 55, and magnetic sensors 58 and 59 are mounted on wiring board 57 in respective positions confronting permanent magnets 54 and 56.
When the steering shaft rotates, rotary body 51, detector body 53 and detector body 55 also rotate in a linked motion with the steering shaft. Magnetic sensors 58 and 59 detect the rotations of permanent magnets 54 and 56 respectively, and send detecting signals to control circuit 60 provided with a microcomputer. The detecting signals of magnetic sensors 58 and 59 differ in cycle and phase from each other because the numbers of cogs are different between gears 53A and 55A.
Control circuit 60 calculates a rotation angle of rotary body 51, that is, the rotation angle of the steering shaft, by executing a predetermined operation according to the two detecting signals and the numbers of cogs of the respective gears. The prior art technique discussed above is shown in Japanese Patent Unexamined Publication, No. 2005-3625.
In the conventional rotation angle detector discussed above, however, there is a problem that it is difficult to detect the rotation angle with high accuracy because rotary body 51 rotates eccentrically due to a gap between cylindrical portion 51C and opening 52A.